126 Interference of mastitis with ovulation and oocyte and granulosa cell quality in dairy cows

Abstract

The objective of this study was to evaluate the effect of mastitis diagnosed by somatic cell count (SCC) on follicular growth, ovulation, oocytes and cumulus cells quality and the concentration and size of exosomes in follicular fluid of dairy cows. In the study, crossbred cows (Bos taurus-Holstein×Bos indicus-Gir) were classified for analysis as control (SCC <200.000 cells mL−1) and mastitis (SCC >400.000 cells mL−1) groups. In Experiment 1 (follicular dynamics), cows (n=57: control=31; mastitis=26) received a progesterone intravaginal device (Sincrogest®, Ourofino Saude Animal, Cravinhos, Brazil) and 2mg of oestradiol benzoate (Sincrodiol®, Ourofino Saude Animal) injected IM. Eight days later (D8), the progesterone device was removed and cows received IM 500mg of cloprostenol (Sincrocio®, Ourofino Saude Animal), 1mg of oestradiol cypionate (SincroCP®, Ourofino Saude Animal) and 300IU of eCG (SicroeCG®, Ourofino Saude Animal). Ultrasound exams (Mindray 4900, probe linear de 5MHz, Shenzhen, China) were performed every 24h from removal of the progesterone-releasing intravaginal device (D8) until 48h later. Thereafter, evaluations were performed every 12h, until ovulation or up to 96h after removal of the progesterone-releasing intravaginal device. In Experiment 2 (oocyte, cumulus complexes, and follicular fluid evaluation), cows (n=26: control=13; mastitis=13) were submitted to follicular aspiration (ovum pickup) for oocyte quality and cumulus cells transcript evaluation. Transcript abundance of apoptosis markers (BCL2, BAX, PI3K, PTEN, FOXO3) was determined by real-time RT-PCR. Moreover, 7 days after the ovum pickup session, the dominant follicle was aspirated and follicular fluid samples were obtained. Exosomes were isolated from the follicular fluid by serial centrifugations, which were also performed for evaluation of particle size and concentration. Statistical analyses were performed using the SAS (SAS Institute Inc., Cary, NC, USA), and the GLIMMIX procedure was used to determine significant differences between groups. Gene expression and exosome data were submitted to the Student’s t-test. Ovulation rate [control 77.4% (24/31) and mastitis 57.7% (15/26); P=0.09] and viable oocytes rate [control 59.1% (130/220) and mastitis 41.9% (125/298); P=0.01] were higher in control animals. Additionally, there was a greater number of degenerate oocytes (control 6.7±1.2 and mastitis 13.3±5.5; P=0.001) in subclinical mastitis cows. There was greater abundance (P=0.003) of BAX cumulus cell transcripts and exosome mean (P=0.03) was smaller in subclinical mastitis cows. However, BCL2, PI3K, PTEN, nd FOXO3 cumulus cell transcripts was similar between treatments. In conclusion, ovulation rate, oocyte quality, and exosome diameter were smaller in cows with SCC >400.000 cells mL−1, demonstrating that subclinical mastitis can influence the fertility of dairy cows.